In the Eastern liturgies, the names for this office in the various languages also mean "first (hour)", based upon the traditional methods of calculating the hour of the day. In Ancient Rome, the period of daylight was divided into 12 hours, but the length of each hour would change depending upon the season of the year.[citation needed] In the Ethiopian Orthodox Church, in some monasteries the times of the services are still calculated by the shadow of the sun to this day.[citation needed]

This short office is one of those whose origin is best known. Saint John Cassian, speaking of Prime, says expressly "sciendum . . . hanc matitutinam canonicam functionem nostro tempore in nostro quoque monasterio primitus institutam." ("it is to be known . . . this morning canonical function [i.e. Prime] was first instituted in our time and in our monastery").[3]

As the chronology of Cassian's works has recently been established fairly accurately, the institution of Prime must be placed towards 382.[4] Apropos of this monastery, of which Cassian speaks as the cradle of Prime, it has now been proved that it was not St. Jerome's monastery at Bethlehem, but another, perhaps one established beyond the Tower of Ader (or of the Flock) beyond the village of the Shepherds, and consequently beyond the modern Beth-saour; it has been identified either with Deïr-er-Raouat (convent of the shepherds) or with Seiar-er-Ganhem (enclosure of the sheep).

We learn further from Cassian the reason that led to the institution of this office. The office of the night, comprising Matins and Lauds, ended then at sunrise, so that Lauds corresponded to the dawn. After the night offices at Bethlehem, as in the other Palestinian monasteries, the monks might retire afterwards to rest. As no other office called them together before Terce (Third Hour), those who were lazy seized the opportunity of prolonging their sleep till nine in the morning, instead of applying themselves to manual work or spiritual reading. To end this abuse, it was decided, in the above monastery, to continue the custom of reposing after the night office, but, to prevent an undue prolongation of sleep, the monks were recalled to choir at the hour of Prime, and after the recital of a few psalms they were to work until Terce.[5] All this is established by authentic texts. The only difficulty is that some contemporaries of Cassian or even his predecessors, such as Eusebius of Caesarea, St. Jerome, St. Basil, St. John Chrysostom, speak of an office recited at sunrise, and which therefore would seem to be identical with Prime. But they are speaking of Lauds, which in some communities was recited later, and so was identified with the hour but not with the subject matter of Prime.

The matter composing the new hour was drawn from the office of Lauds; or rather Prime, as an office, was a repetition of part of Lauds, and added nothing to the ensemble of the psalmody, only Psalms 1, 57 (58), and 89 (90), which were formerly part of Lauds, were recited at this hour. Such at least was the original composition of Prime; but the monasteries which gradually adopted it in the East and in the West changed its constitution as they liked. It is impossible to describe here all the variations this office underwent in the different liturgies. We need only remark that one of the most characteristic features of Prime is the recitation of the famous symbol "Quicumque vult salvus esse", called the Athanasian Creed, which has recently been the subject of much controversy in the Anglican Church.[citation needed]St. Benedict orders to be recited at Prime on Sundays four groups of eight verses of Ps. 143 (144); on week-days, three psalms, beginning with the first and continuing to Ps. 19 (20), taking three psalms each day (Ps. 9 (10) and 17 (18) being divided into two). In that way Prime is symmetrical, like the other Little Hours of the day. It resembles these also in composition, the psalmody being accompanied by a hymn, an antiphon, capitulum, versicle, and prayer. In the Roman Liturgy the office of Prime is not composed so symmetrically. Usually it consists of Ps. 53 (54), 107 (108), the first four groups of eight verses of Ps. 118 (119), and during the week Pss. 53 (54), 23 (24), 25 (26), 24 (25), 22 (23), and 21 (22). The capitulum and other elements are after the model of the Little Hours (cf. None). In the Anglican Church, the Office of Prime was lost in the publication of the Book of Common Prayer; however, the 1928 version of the Book of Common Prayer (which was accepted by the Church, but rejected by Parliament) restored Prime, with the instruction that it must be used in addition to (not instead of) Matins, and with the option of reciting the Athanasian Creed.

So far we have spoken only of the office of Prime properly so called, which ends like the other Little Hours. It is followed by some prayers which are called the office of the chapter, and are composed in the Roman Liturgy of the reading of the martyrology, of a prayer, "Sancta Maria et omnes sancti" ("May holy Mary and all the Saints..."), a prayer concerning work, "Respice in servos tuos . . . Dirigere et sanctificare" ("Look upon thy servants... Direct and sanctify"), and a blessing. This addition to Prime is a legacy bequeathed by the monks to the secular clergy. As has been said above, originally after Prime the monks had to betake themselves to manual work or reading. The office therefore ended with a prayer for their work "... et opera manuum nostrarum dirige super nos et opus manuum nostrarum dirige" ("...and direct thou the works of our hands over us; yea, the work of our hands do thou direct."), and the prayer "Dirigere". Later the reading of the martyrology, the necrology, the rule, and a prayer for the dead were added.[6]

In view of its origin and constitution, Prime is to be considered as the prayer of the beginning of the day, whereas Lauds is devoted to recalling with the dawn the memory of Christ's Resurrection, Prime is the morning hour which consecrates all the work of the day. Its institution has made the liturgical day more regular and symmetrical. Prime, until then without an office, received its psalmody like Terce, Sext, None, Vespers. With Compline and Lauds, the liturgical day reached the sacred septenary, "septies in die laudem dixi tibi" ("seven times a day I have given praise to thee)", while for the night office there was the text: "media nocte surgebam ad confitendum tibi" ("I rose at midnight to give praise to thee").

In the Eastern Orthodox and Greek Catholic Churches the office of the First Hour is normally read by a single Reader and has very little variation in it. Three fixed psalms are read at the First Hour: Psalms 5, 89, and 100 (LXX). The only variable portions for most of the year are the Troparia (either one or two) and Kontakion of the Day. Whereas the other Little Hours are normally followed by other services, the First Hour is normally read immediately after Matins and so it is concluded with a dismissal by the priest. In the Russian usage, the dismissal is followed by a hymn to the Theotokos (the Kontakion of the Annunciation, Tone 8):

"To thee, the champion leader, we thy servants dedicate a feast of victory and of thanksgiving, as ones rescued out of sufferings, O Theotokos; but as thou art one with might which is invincible, from all dangers that can be do thou deliver us, that we may cry to thee: Rejoice, thou Bride Unweded!"

During Great Lent a number of changes in the office take place. On Tuesday, Wednesday and Thursday, after the three fixed psalms, the Reader says a kathisma from the Psalter. The Troparion of the Day is replaced by special Lenten hymns that are chanted with prostrations. Then the psalm verses that follow the Theotokion, which are normally read, are instead sung by the choir. The Kontakion is also replaced by special Lenten hymns which are sung. Near the end of the Hour, the Prayer of St. Ephraim is said, with prostrations.

On Monday, Wednesday, and Friday of the Fourth Week of Great Lent, the Veneration of the Cross takes place at the First Hour.

During the Fifth Week of Great Lent, there is a kathisma only on Tuesday and Wednesday, due to the reading of the Great Canon of Saint Andrew of Crete on Thursday morning. If, however, the Great Feast of the Annunciation falls on that particular Thursday, the reading of the Great Canon will be moved to Tuesday and, as a result, a kathisma will be read on Monday, Wednesday and Thursday.

During Holy Week, on Monday, Tuesday and Wednesday, the services are similar to those during Great Lent except there is no reading of Kathismata, and instead of the normal Lenten hymns which replace the Kontakion, the Kontakion of the day (i.e., that day of Holy Week) is chanted. On Great Thursday and Saturday, the Little Hours are more like normal, except that a Troparion of the Prophecy, prokeimena, and a reading from Jeremiah are chanted at the First Hour on Great Thursday. On Great Friday, the Royal Hours are chanted.

During the Lesser Lenten seasons (Nativity Fast, Apostles' Fast and Dormition Fast) the Little Hours undergo changes similar to those during Great Lent, except the hymns are usually read instead of chanted, and there are no kathismata on weekdays. In addition, on weekdays of the Lesser Fasts, the Inter-Hour (Greek: Mesorion) may be read immediately after the First Hour (at least on the first day of the Fast).[7] The Inter-Hours follow the same general outline as the Little Hours, except they are shorter. When the Inter-Hour follows the First Hour, the dismissal is said at the end of the Inter-Hour rather than at the end of the First Hour.

When the Royal Hours are chanted (the Eve of Nativity, the Eve of Theophany and Great Friday), the First Hour is not joined to Matins as normal, but it becomes the first office in an aggregated office composed of the First, Third, Sixth and Ninth Hours and the Typica. This is the most elaborate form of the First Hour. Both the priest and deacon are vested and serve, and the Gospel Book is set on an analogion (lectern) in the center of the temple (church building). At the beginning of the First Hour, the deacon performs a full censing of the church, clergy and faithful. Two of the three fixed psalms (89 and 100) are replaced by others that are appropriate to the particular feast day being celebrated. A number of hymns (stichera) are sung in place of the Troparion of the Day. Then a prokeimenon, the reading of a relevant Old Testamentprophesy, an Epistle and a Gospel are chanted. The Kontakion of the Day is chanted by the choir, instead of being read. Since at the Royal Hours other services immediately follow the First Hour, there is no dismissal.

In the Armenian Liturgy, the office following the Morning Hour is called the Sunrise Hour (Armenian: Երեւագալ Ժամ yerevagal zham). The Armenian Book of Hours (Zhamagirk`) states that this service is dedicated “to the Holy Spirit and to the resurrection of Christ and to [his] appearance to the disciples.”

Outline of the service

Introduction: “Blessed is our Lord Jesus Christ. Amen. Our father...”

First station: Psalm 72:17-19 “Glory...Now and Ever...Amen.” “Again and again in peace...Accept, save, and have mercy.” “Blessing and glory to the Father...Amen.” Sunrise Hymn attributed to St Nerses: “From the East...(Arewelits`...)” Exhortation: “From the East unto the West, children of Sion...” Proclamation of Sunrise, to follow the hymn and the canon, composed by Giwt: “From the East unto the West in all parts of Christendom...” Prayer: “From the East unto the West you are praised...”

The various Oriental Orthodox and Oriental Catholic Rites will vary in the particulars of the First Hour, but in general tend to have a larger number of psalms in them. In some Rites it is the practice to recite the entire Psalter once a day (as opposed to once a week, as in the Western and Constantinopolitan Rites).

The East Syrian Rite does not have a separate service of First Hour, having only three daily services in their office: Evening, Morning and Noonday.